Hydraulic master brake cylinder having bleeding means



M. V. G ROVES Oct. 28, 1952 HYDRAULIC MASTER BRAKE CYLINDER HAVINGBLEEDING MEANS 2 SHEETS-SHEET 1 a v 6 mm 5 T zrN M m VV T m M T E mFiled Nov. 29. 1949 M. v. GROVES 2,615,304

HYDRAULIC MASTER BRAKE CYLINDER HAVING BLEEDING-MEANS Oct. 28, 1952Filed Nov. 29, 1949 2 SHEETS--SHEET 2 m N R 0 IN VEN TOR.

Patented Oct. 28, 1952 HYDRAULIC MASTER BRAKE CYLINDER HAVING BLEEDINGMEANS Martin V. Groves, Brooklyn, N. Y. Application November 29, 1949,Serial No. 130,005

(o1. GO-54.6)

10 Claims.

This invention relates to fluid pressure braking systems and, moreparticularly, to hydraulic brake master cylindersv of .the horizontaltype for use in such systems.

In hydraulic'brake systems hitherto known or used, it has been thegeneral practice, where a horizontal type master cylinder is employed,to place the cylinder in communication with a liquid reservoir throughboth a supply port and a compensating port for removing air trapped inthe cylinder. The compensating port is so positioned that with thepiston in its fully retracted position, the port is disposed slightlyahead of the sealing cup carried on the piston head. As the pistonmovesthrough its protractile stroke to compress the fluid within thecylinder, the resultant pressure generated at the piston head expandsthe sealing cup such that it tendsto enter the compensatingport as itmoves thereacross with the result'that it becomes worn and, in .someinstances, is torn and its sealing effect is, greatly diminished. Thepresent invention aims to overcome this disadvantage by eliminating thecompensating port from the master cylinder structure. P

Another object of the'invention is the provision of anew and improvedmaster cylinder in which gases,'usually air, trapped within thecylinder, are syphoned off into'the fluid reservoir during the movementof the piston.

A further object is to provide anew and improved master cylinder whichissimple in construction, readily fabricated and assembled, andeconomical to manufacture. The invention will now be described indetail. by reference to the accompanying drawings in which;

Fig. 1 is a sectional view, taken on a vertical plane "passing throughthe axis of the cylinder, of an hydraulic brake master cylinderincorporating the features of the invention and in which the variousparts'are shown in their normal, unoperated positions;

Fig. .2 is a view in section-taken along the line 2-2 of Fig.1;

Fig. 3 is an enlarged fragmentary view of a. part ofthe cylinder ofFig.1 showingrclearly the path over which the brake fluid may flowduring the operation of the cylinder; and, 1

Fig. 4 is a fragmentary horizontal sectional view showing alternativemounting means for the cylinder.

In the form shown in Fig. 1 of the drawings, the invention comprises a,cylinder barrel 2 composed of steel tubing/the forward end of whichreceives 1 2 an end cap 3 held in place by means of an end cap nut 4,the end cap being provided with a central opening 5 therethrough, whichserves as a fluid pressure delivery port for conducting fluid underpressure to the respective wheel brake 7 cylinders, in a manner wellknown in the art. The rear end of the cylinder barrel 2 is provided withan annular flange 6 which overlies a mounting plate I disposed about thecylinder barrel. A clamping plate 8 is placed in face-to-face engagementwith the annular flange 6 of the cylinder barrel 2 and the mountin plateI and is secured to the mounting plate as by the screw 9. The mountingand clamping plates are composed of stamped sheet metal and jointlyserve as a detachable bracket assembly by means of which the cylindermay be mounted or supportedin an automobile, for example. v

A piston generally indicated at H] is reciprocable within the cylinder 2and includes a main body portion I l composed of stamped sheet metal andan annular detached head l2 spaced apart from the main body portionwhereby the main body portion of the piston during the initial por: tionof its protractile movement may move with respect to the detached head.In the unoperated position shown in the drawings, the detached pistonhead l2 rests against astop ring [3, fixed against axial displacement,as by being seated in a recess in the cylinder barrel 2, while the rearend of the main body portion ll thereof rests against the clamping plate8; which serves as a stop therefor. Hydraulic fluid for the cylinder 2is supplied from a reservoir l4 composed of stamped sheet metal andcarried on the cylinder, the reservoir having'a-filling opening l5normally closed by a plug 16 provided with openings I! for venting thereservoir to atmosphere. The cylinder 2 and the. bottom of the reservoir[4 are provided with aligned openings I8 and l8,-re spectively, locatedrearwardly of the detached piston head i2 and through which extends abolt MI-adapted to receive a nut 2| and thereby to clamp togethersecurely thereservoir and cylinder. A suitable ring 20"is disposed aboutbolt 20 in order to provide a fluid-tight sealbetween the cylinderbarrel 2 and reservoir 14. ,A s-ese en in Fig. 2 of the drawings, thereservoir [4 has its bottom, forwardly and rearwardly of the nut 2 I,channeled out to receive the upper convex surface of the cylinder 2;therebyproviding, when secured in place by the bolt 20 and nut 2|, meansfor preventing angular movement of the .;reservoir. Fluid is admittedfrom the reservoir to the cylinder rearwardly 0f thedetached piston headl2 3 by means of a port 22 which extends centrally through the bolt 20.

A primary sealing cup 23 seats both on the detached piston head [2 andon the inner wall of the cylinder barrel 2 and is provided with anannular flange 24 which projects intermediat the annular detached pistonhead and a reduced diameter portion 25 of the main body of the pistoninto, an annular fluid passage 26 formed therebetween. Valve controlmeans for the fluid passage is provided by a valve seat Ha formed on themain body portion I I of the piston by the reduced portion thereof,andwhich seats on' the annular flange 24 of the primary cup. 23 to sealoff the passage 26 upon predetermined protractile movement of the mainbody portion of the piston. A secondary sealing cup 27 is disposed aboutthe rear end of the main body portion H of the piston inorder to preventseepage of fluid from the rear end of th cylinder past the piston. Thecup 21 1s seated in an annular recess in the main body portion H of: thepiston whose rear extremityis provided with an enlarged-diameter flange.

Seated against the primary sealing cup 23 is a bleeder retainer 28having a circular flange portion 29 which serves to define front andrear chambers 2a and 2b, respectively, of the cylinder; The diameterofthe circular flange 29. is slightly lessthan the bore of the cylinderbarrel 2 m order that fluid may flow between the front and rear cylinderchambers 20, and 2b, respectively, when'the annular flange 24 of theprimary cup 23 and valve seat Il a are not in sealing'engagement. Aplurality of'indents, such as 30, are formed in the circular flange 29through which fluid may flow between flange 29 and the primary cup 23 soas to passbetween the 'r'eservoir'M and the frontcylinder chamber 2awhen the parts are in their normalunoperated "positions? A bleeder cupseal'3 lis disposed within the-=bleeder retainer 2-8-and is seatedagainst the rounded forward end 32 of the main'body por tionl lyof thepiston so as to be responsive to protractile movementthereof fordisplacing fluid from thefront cylinder chamber 2a by way of anopening33 in the front end'of the-bleeder re+ tainer. The bleeder cup seal 3lis yieldablysupported byacoil compression spring 34 whose respectiveends are's'eated on the bleeder retainer za'and on" the bleeder cup. Thebleeder flange 29 and bleeder seal 3 ljointly provide a bleeder cap.

Thebleeder retainer 28 is yieldably maintained in an initial unoperatedposition by means of a coil compression spring 35 whose respective endsareseated' on the; circular flange of the bleeder retainer'and on avalve retainer 36 which forms one element of a two-way line pressurevalve. it valve seal 37 carried on .the valve retainer 36,'a-nd-disposed'over the fiu'id pressure delivery port 5} forms the"other element of the line pressure valve. The valve retainer 36-isprovided witha plurality ofopenings, suchas 38; through whichfluid-under pressure passes to engage a flexible annular lip 3 9-onthe;valve seal 31 with the result that the annular lip which normallyseats against the-valve-retainer, as shownin' the drawings, is moved outof" engagement therewith to permit the-fluid under pressureto passthrough the dc liverypert 5. v

' An actuating shaft is disposed within the hOllOW- main body portion I[of the piston}! 0 and carries at-the rear end thereof a suitablecoupling' member 41" which may, for example, be connected to alinkage-mechanism "(not shown) 4 manually operable to drive the pistonthrough its protractile stroke. A boot 42 is employed to prevententrance into the cylinder of dust, grit, dirt, and the like, and issupported at its opposite ends on the clamping plate 8 and .the couplingmember 4 I.

The operation of the invention will now be described and for thispurpose, it is assumed that the reservoir [4 is filled with a suitablehydraulic brake fluid and that the various component parts of theinvention are in their normal unoperated positions, as shown in thedrawings. With-the parts in their normal unoperated positions, fluid isadmitted from the reservoir l4 to the front chamber 2a of the cylinderby way of port 22, annular passage 26, the plurality ofiindents 30 onthe circular flang 29 of the bleeder retainer 28 and around theperimeter of 'the circular flange itself. Upon inward movement of theshaft 40, the main body portion ll of the piston begins its protractiletstroke and during. the initial portion-thereof, it movesv with respectto the detached headn|2 of the piston. When .this occurs, the reducedendof the piston body H and the bleeder cup seal 3| are. drivenwithinthe bleeder retainer'28 by the main body portion H of the pistonto displace, fluid in the front chamber 2a of the cylinder. Thisdisplacedfluid is caused to flow back intothe reservoir I l over. the.following. path; around .the perimeter of the circularrflange 29-on1 thebleeder retainer 28, through the plurality of indents.30 in thecircularjfiange, through the: annular pas sageZfi between the. detachedhead. l2 and main body portion H of: the piston and through. the port.22. It is wellknown that air in the system ac'cumulates in the. mastercylinder. The velocity of thefluid' flowing between the circularfiange29: of the bleeder-retainer 28v and the wall of 1 the. cylinder barrel2: is adequate to entrain: airbubbles present within. the cylinder.- andsyphon' them. off into there'serVoir I4 through the path above.described; .The. detached piston head-.12 and:primary cup 231carriedthereon, as well as the bleeder retainer 28, are prevented from movingduring. the initial. protractile, movementiof the main body; of thepiston by the coil spring 3.5 which, being-substantially stiffer'thanthe: coil spring 34;. yieldably maintains-these members in afixedposition.

.The displacementsof fluid from the. cylinder back to the fluidreservoirecontinues; untilthe protractile. movement of: the; main' bodyof the piston is such as to: cause the valve. seat Ha formed thereontozsea'l againstithe annular flange 24 bit the-primary cup 23". Whenthis. occurs,

the annular passage 26 is sealed off and the detached; piston head I2 isengaged and driven.- by the main: body ofa-theipiston to displacezfluidunder! pressure through theideliveryport 5 by wayof theitwo-wayslinepressure valve 361-39 It will be understood 'that sufii'cient: pressure1 is not developed withintthelfront chamber 2a of the cylindertooperatethe two-way line pressure valve until after the annularpassageZGKha-s been sealed off; thereafter,: the-pressure; developedwithin the front'chamb'erof the cylinder-iscommunicat'ed throughopenings 3 8:' in the. valve :retainer 36 to the flexibl'e' annular lip.39 on the valve: seal 3.! toiwcauseithealipto become disengaged from:the retainer,- thereby. providing-2 for the free flow of fluid underpressure to thetdeliveryport5. 1. 2

When the actuating shaft 40'is retractedfrom its a/ppli'ed position, a:pressure. dro is. pro:-

the line pressure valve.

12 and main body portion ll of the piston to restore them to theirinitial unoperatedpositions shown in the drawings, the detached headbeing'thereafter maintained in its unoperated position by the coilspring 35, and the main body portion of the piston being thereaftermaintained in its unoperated position under the influence of .the coilspring 34.

When an hydraulic master brake cylinder is first installed in a brakesystem for use, it is the usual practice to perform what is calleda'bleeding operation thereon and which consists in reciprocating thepiston several times inorder to syphon off any air which may be trappedwithin the cylinder. According to the present invention, this bleedingoperation takes place during retractile as well as protractile movementand the former is rendered materially more efficient by the use of atwo-way line pressure valve of the type disclosed in conjunction withthe bleeder means. It will be noted that the area of the valve retainerelement 36 of the line pressure valve is less than the area of theprimary cup 23 carried by the detached piston head l2 such that when thepiston is reciprocated to bleed the brakes, the suction produced in thefront chamber 2a. of the cylinder on the retractile stroke of the pistonwill cause the primary cup to become unseated from the detached head ofthe piston, thereby opening the annular passage 26. At this point,

however, the valve seal 31 of the line pressure valve will remain on itsseat and cause the brake system to become overloaded with fluid flowingto the master cylinder from the reservoir, However, when the pressure inthe brake system is sufficient a valve seal 31 will be unseated andthereby open If the retractile movement continues at a sufficient rateto maintain suction in the forward cylinder chamber 2a the fluid willcontinue to be pulled from the reservoir into the forward chamber 2auntil the detached head I2 strikes the stop ring l3; whereupon continuedretractile movement of the piston body I I,

under the influence of bleeder spring 34 will hold the seat Ila awayfrom the primary sealing lip 24. The suction chamber 2a having thenceased and the system being overloaded, the fluid from I the brakesystem (under the influence of the released pressure in the system) isforced past the circular flange 29 of the bleeder retainer 28 andthrough the annular passage 26 to the reservoir 14, the velocity of thefluid flowing past the cir-' cular flange being adequate to entrain andcarry any 'air bubbles which may have been present within the system.

,. In .the'form of the invention illustrated and described, thepossibility of air being trapped within the cylinder is greatlydiminished, if not -excluded entirely, since the cylinder is bleededeach time the piston is driven through its protractile stroke, as wellas on the retractile stroke -under the conditions just described.Moreover, by

eliminating the compensating port and providing a single fluid supplyport between the reservoir and cylinder'and locating this portrearwardly of the piston head, the susceptibility to damage ofbeen thepractice to construct the master cylinder ,of a metal casting requiringmany individual suc- .cessive machining operations on the same piece.

This not only has been-costlyin time and tooling but the resultantdevice was greater in weight. By my invention, the parts may beindividually made and then assembled and the resultant product ismaterially lighter in weight and may be roduced at a fraction of thecost of prior devices.- v

It will be noted that the bracket assembly, comprising plates 1 and 8,for mounting the master cylinder has been located to support it at therear end thereof, as is required for many installations. There are,however, other installations in which'the master cylinder should besupported at its side and, therefore, alternative mounting meanssuitable for such installations is shown in Fig. 4; of the drawings. Itwill be seen that the end cap-3.:is provided with a reduced portion 43atfthe, outer extremity thereof in order to form an annular groove 44between the end cap and the end cap nut 4. To support the cylinder atits side, a sidebracket member 45 is provided, one end of which isprovided with a circular flange 46 which slides over the cylinder barrel2 to engage the annular flange B at the rear end thereof, The other endof the bracket member 45 also is provided with an annular flange portion41 v which engages within the annular groove 44 whereby the bracketmember is made. secure to the cylinder at the forward end thereof. Tosecure the bracket member 45 to the cylinder at the rearend thereof, aplate member 48 isplaced over the annular flange 6 on the cylinderbarrel 2 and issecured to the circular flange 46 of the bracket memberas by screws 49, the platemember 48 also serving as a support for theprotective boot 42, asdescribed above. For convenience inmanufacture andassembly, the bracketmember 45 'and plate member 48 are composed ofstamped sheet metal which does away with many costly finishingoperations, as heretofore described. Thus, instead of having to make andstock separate master cylinder assemblies for the therein withoutdeparting from the spirit and scope of the invention, as defined by theclaims appended hereto.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:

1. An hydraulic brake master cylinder comprising, a cylinder, a pistonmovable therein for producing fluidpressure to operate the brakes, anhydraulic fluid reservoir in fluid communication with said cylinderrearwardly of the head of said piston when the piston is in its fullyretracted 7 position, fluid passage means forsconveyin'g fluid forwardlyof the head of said piston, said piston being adapted to seal on saidfluid passage upon predetermined protractile movement thereof; ableeding member in saidcylinder forwardly of the head of said piston andhaving a circular flange of smaller diameter than the bore of thecylinder, and means responsive toprotractile movement of said piston fordisplacing hydraulic fluid from the cylinder around the perimeter'ofsaid circular flange and through said fluid passage to said resevoi'runtil the fluid passage has been sealed off by the piston, thereby tosyphon on gases trapped within the cylinder. 1 I

- 2. An hydraulic brake master cylinder comprising, a cylinder, a pistonmovable therein for producing fluid pressure, anl'iyd'raulicfluidre'se'rvoir, fluid passage means for admitting fluidfrom said reservoir tosaid cylinder, said-piston being adapted to sealoff said fluid passage upon predetermined protractile movement thereof,a bleeding member in said cylinder spaced forwardly of the head-of saidpiston and having a circular flange of a diameter smallertnan thecylinder bore, means responsive to protractile movement of said pistonfor displacing hydraulic fluid from the cylinder around the perimeter ofsaid circular flange and through saidiliiid passage to said reservoiruntil said fluid passage has been sealed off by the piston, thereby tosyphon off gases trapped Within the cylinder, and means for maintainingsaid bleeding member in a fixed position until said fluid passage hasbeen sealed off by said piston.

3. An hydraulic brake master'cylinder comprisin a cylinder, a bleedingmember disposed Within said cylinder and having a circular flange of adiameter smaller than the bore of the cylinder, said bleeding memberdividing said cylinder into front and rear chambers, an bydraulic fluidreservoir in fluid communication with the rear chamber of the cylinder,fluid pasvoir, the fluid passing around the*'fl'ange'- of the bleedingmember and through said fluid passage, thereby to syphon off gasestrapped in thefront chamber of the cylinder.

4. An hydraulic brake master cylinder comprising, a cylinder, a pistontherein in'cluding a main body portion and a detached head, said bodyportion being movable first with respect to and thereafter with saiddetached head, an hydraulic fluid reservoir co-mmuni'catingiwith saidcylinder rearward'ly oflthe detached head of said piston,'the spacebetween the main body portion and detached head of said piston providinga fluid passage, and bleeding means including: a circular flange ofsmaller diameterl'thanthe bore of said cylinder, said bleedingmeansbeing, responsive to relative movement between the main body portion anddetached head of said piston for displacing fluid from said-cylinderaround the circular flange of said bleeding-'means and through saidfluid passage to said fluid reservoir, thereby to syphon offgasestrappediw-ithin the forward portion'of the cylinder.

8 5-.VAn hydraulic brake master cylinder cornprising, a-cylinder, ableeding member therein dividing the cylinder into front andrearchambers, said bleeding member being provided with a circular flange ofa smaller diameter than the bore' of said cylinder, an-hydraulicfluidreservoir communicating with the rearchamber of said cylinder, apistonin said cylinder, said piston inc ludi-ng a main body portionand-adetached head, said; body portion being movable withand with respect tosaid detached head, the space between the main body portion and-detachedhead of said piston providing a fluid passage betweerrthe front and;rear chambers of said cylinder, and meansresponsive'to' relativemovement between the main body portion of said piston and thedetachedhead thereof for displacingv fluid from the front chamber ofsaid cylinder into said reservoir, the displaced fluid flowing aroundthe circular flange of said bleeding member and through said fluidpassage into the rear chamber of said cylinder, thereby to syphon offgases trapped in the front chamber of the cylinder.

6; An hydraulic brake master cylinder comprising, a cylinder, apistonmovable therein for producing fluid pressure and comprising abody anddetached head, said piston body and head 1 jointly providing. a firstvalve, resilient means urging said head rearwardly toward said pistonbody to close said valve, a stop limiting the rearward movement of saidhead to openv said valve near the end of the retractile stroke of saidpiston body, a reservoir in fluid communication with said cylinderrearwardly of said valve, and a bleeding member disposed within saidcylinder forwardly of and in spaced relation to said head, said memberand cylinder Wall providing therebetween an annularly disposedrestricted passageway, whereby the passage of liquid rearwardly.therethrough will be of such velocity as to siphon air from thecylinder chamber forwardly of said head through said valve and pass itinto said reservoir.

7. An hydraulic master brake cylinder comprising, a cylinder, a pistonmovable in said cylinder, said'pistonincluding a body and a detachedhead having a valve portion engageable with a complementary portion ofsaid body to provide a valve, an hydraulic fluid reservoir'in fluidcommunication with said cylinder rearwardlyof'thehead of' said piston atall times, fluid passage means including said valve for conveying fluid;from one side of the head of said piston to the other side, said valvebeing operable to closed position by the protractile movement ofsaidpiston body and to open position by the retractile movement ofsaidpiston body, and bleeding means providing a restricted passage wayat the peripheral wall of said cylinder adjacent the front of said headand in communication with said valve, whereby fluid flowing from thecylinder in front of said head through said valve and into saidreservoir will siphon off gases trapped within said cylinder due to" thevelocity of flo'w through said restricted bl eeder passageway.

8'. An hydraulic brake master cylinder comprising, a cylinder, a bleedermember disposed Within said cylinder and having a, circular flange of adiameter smaller than the bore-of saidcylinder, said bleeder memberdividing-said cylinder into front and rear ch'amb'ershaving a restrictedperipherally disposed: interconnecting bleede'r passage,- a liquidreservoir communicating with the rear: chamber of said'cylindena pistonin said rear chamber, said piston comprising a body whose forward end isprovided with a shoulder serving as a valve seat and an annular detachedhead provided with a valve portion for engagement with said seat and aperipheral portion for sealing engagement with said cylinder wall, saidhead and said bleeder member being in spaced relationship to therebyprovide fluid communication between said valve and bleeder passage, acompression spring in said forward chamber urging said bleeder memberand head toward said piston body and said valve portion toward its seat,a limit stop restricting rearward movement of said head to thereby opensaid valve upon further retractile movement of said piston body, andresilient means more readily yieldable than said spring urging saidpiston body valve seat away from said piston head valve portion to opensaid valve.

9. An hydraulic brake master cylinder comprising, a cylinder, a pistonmovable therein for producing fluid pressure and comprising a body anddetached head, said piston body and head jointly providing a firstvalve, a reservoir in fluid communication with said cylinder rearwardlyof said valve, a bleeding member disposed within said cylinder forwardlyof and in spaced relation to said head, said member and cylinder wallproviding therebetween an annularly disposed restricted passagewaywhereby the passage of liquid rearwardly therethrough will be of suchvelocity as to siphon air from the cylinder chamber forwardly of saidhead through said valve and pass it into said reservoir, a line valve inthe outlet end of said cylinder and having an effective area less thanthe effective area of said piston head, a common compression springinterposed between said line valve at one end and said bleeder memberand piston head at its opposite end for urging said line valve and firstvalve to closed position, a stop for limiting the rearward movement ofsaid head to thereby open said first valve near the end of theretractile stroke of said piston body, and resilient means interposedbetween said bleeder member and piston body providing greater resiliencythan said spring and operable to urge said valve to open position.

10. An hydraulic master brake cylinder comprising, a cylinder, a pistonmovable in said cylinder, said piston including a body and a detachedhead having a valve portion engageable with a complementary portion ofsaid body to provide a first valve, an hydraulic fluid reservoir influid communication with said cylinder rearwardly of the head of saidpiston at all times, fluid passage means including said first valve forconveying fluid from one side of the head of said piston to the otherside, a line valve in the outlet end of said cylinder, common resilientmeans for urging said first valve toward its seat and said line valve toclosed position, said line valve being of less effective area than theefiective area of said first valve, whereby said first valve will openunder a lower suction than said line valve upon retractile movement ofsaid piston and admit overloading fluid into said cylinder from saidreservoir before said line valve opens to admit fiuid to said cylinderfrom the system, a stop limiting the rearward movement of said head toopen said first valve near the end of the retractile stroke of saidpiston body, and bleeding means providing a restricted passagewayadjacent the peripheral wall of said cylinder contiguous with said headand in communication with said first valve, whereby when line pressurefluid opens said line valve displacing iluid from said cylinder throughsaid first valve to said reservoir said displaced fluid will flowthrough said restricted bleeding passage at relatively high velocity andsiphon ofi gases trapped in said cylinder.

MARTIN V. GROVES.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,211,652 Gardner Aug. 13, 19402,255,359 Lepersonne Sept. 9, 1941 2,352,920 Stevens July 4, 19442,357,386 Dick Sept. 5, 1944

